JP2914093B2 - Semiconductor laser - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a semiconductor laser,
The present invention relates to a semiconductor laser having a wavelength of 1 μm and suitable for pumping an optical fiber amplifier.

[0002]

2. Description of the Related Art As this kind of semiconductor laser, there is a semiconductor laser using InP as a substrate. In a semiconductor laser using InP as a substrate, a region where light is guided is left in a mesa shape in an active layer formed by epitaxial growth, and current and light are confined by embedding both sides of the mesa portion with a high-resistance semiconductor. A so-called embedded structure is known. On the other hand, in a semiconductor laser using GaAs as a substrate,
It was difficult to make a similar structure. Very recently, a buried semiconductor laser using GaInP as a cladding has been reported, but it is expected that it will be a long time before it is put to practical use in terms of reliability. For this reason, a semiconductor laser using a GaAs substrate has a structure in which an active layer formed by epitaxial growth is left as a whole without being removed by etching, and a current block layer is formed thereabove except for a central current path region. Mainstream.

[0003]

However, in the case of this structure, the difference in the equivalent refractive index in the horizontal direction cannot be made large, so that the light spreads in the horizontal direction, and the spread angle in the horizontal direction tends to be small. . As a result, the ratio (aspect ratio) to the vertical radiation angle becomes large, and it becomes difficult to couple with an optical fiber or the like.

[0004]

A semiconductor laser according to the present invention has GaAs as a substrate and an active layer having a band gap of G.
In a current blocking type semiconductor laser smaller than aAs, a current blocking layer of AlGaInP (including a case where the Ga composition is zero) formed on the main cladding layer on the opposite side of the substrate except for a stripe-shaped current path region; And a GaAs auxiliary cladding layer formed on the main cladding layer in the stripe-shaped current path region sandwiched between the current blocking layers. Further, a second auxiliary cladding layer made of AlGaInP (including a case where either one of Al and Ga is zero) or AlGaAs (including a case where Ga composition is zero) is further provided on the GaAs auxiliary cladding layer. Is desirable. In this case, the thickness of the GaAs auxiliary cladding layer is desirably at least 200 ° or more.

[0005]

Since GaAs, which is a material having a high refractive index, is used as a part of the cladding layer on the opposite side (upper side) of the substrate in the stripe portion (current path region) sandwiched between the current blocking layers, light in this portion is obtained. Are biased to the opposite side (upper side) of the substrate. On the other hand, a material having a low refractive index, A, is used for the current blocking layer.
Since 1GaInP (including the case where the Ga composition is zero) is used, the light confinement effect in the horizontal direction is enhanced in combination with the light distribution of the stripe portion being biased upward. That is, the difference in the equivalent refractive index in the horizontal direction increases.

On the GaAs auxiliary cladding layer, G
AlGaInP, GaIn having a lower refractive index than aAs
When the second auxiliary cladding layer is formed of P, AlGaAs, AlInP, or the like, it is possible to limit the spread of light in the vertical direction. When the light confinement coefficient is reduced by using the GaAs auxiliary cladding layer to spread the light in the vertical direction too much, the laser characteristics may be degraded. In this case, if the second auxiliary cladding layer is used, the light confinement coefficient may be reduced. Reduction is suppressed.

[0007]

FIG. 1 schematically shows a cross-sectional structure parallel to a cleavage plane of a semiconductor laser according to an embodiment of the present invention. FIG. 2 is a table listing the thickness, material, composition ratio of Al to (Al + Ga), impurities, conductivity type, and impurity concentration of each semiconductor layer constituting the semiconductor laser.

To manufacture this semiconductor laser, first,
An epitaxial wafer stacked up to the current block layer 7 is manufactured by reduced pressure MOVPE (metal organic chemical vapor deposition) of about 60 Torr. On a GaAs substrate 1, Ga
As buffer layer 2, n-type AlGaInP cladding layer 3,
Active layer 4, p-type AlGaInP cladding layer 5, p-type Ga
An InP cladding layer 6 and an n-type AlGaInP current blocking layer 7 are formed by epitaxial growth. The active layer 4 has a quantum well structure, and includes a GaInP layer 41, a G
aInAsP layer 42, GaAs layer 43, GaInAs layer 44, GaAs 45, GaInAsP layer 46 and Ga
It is composed of an InP layer 47. In this active layer 4, G
The aInAs layer 44 is a quantum well layer.

In manufacturing this epitaxial wafer, AlGaInP is desirably grown at a high temperature.
Since s is preferably grown at a low temperature, the n-type AlGaInP cladding layer 3 is grown at 740 ° C., and then the temperature is lowered to 650 ° C. to grow the active layer 4. AlGaInP
The current blocking layer 7 is grown.

Next, the central portion of the n-type AlGaInP current block layer 7, which is the uppermost layer of the epitaxial wafer thus formed, is etched and removed in a stripe shape. In this etching, as shown in FIG. 3, first, a silicon nitride film 31 is deposited to a thickness of 0.1 μm on the entire surface, and then the central portion is removed over a width of 3 μm by lithography. Thereafter, the current block layer 7 is etched using the silicon nitride film 31 as a mask. Etching is performed, for example, using concentrated sulfuric acid at 60 ° C. as an etchant until the color of the wafer surface changes. The place where the color of the wafer has changed is where the GaInP layer 6 is exposed.

After that, the silicon nitride film 31 is changed to hydrofluoric acid: water =
Etching at 1: 1 and a p-type GaAs layer 8 thereon
The p-type GaInP layer 9, the p-type GaInAsP layer 10, and the p-type GaAs layer 11 are sequentially regrown. p-type GaAs
In the layer 8, the bottom of the stripe-shaped groove, that is, p-type Ga
The portion formed on the InP cladding layer 6 functions as a part of the upper cladding layer. Further, the p-type GaInP layer 9 thereon further functions as a part of the cladding layer. However, the p-type GaAs auxiliary cladding layer 8 is for raising the light distribution by utilizing its high refractive index, whereas the p-type GaInP second auxiliary cladding layer 9 is made of GaAs. By using the fact that the refractive index is lower than that, the upward spread of light is limited, and the deterioration of laser characteristics is prevented. p-type GaInAsP layer 10 and p
The type GaAs layer 11 is for further reducing the contact resistance with the p-side electrode formed thereon. Since the p-type GaAs auxiliary cladding layer 8 is composed of one group III element, it is advantageous in that regrowth is easy.

Next, a p-side electrode is vapor-deposited on the p-type GaAs layer 11, and the GaAs substrate 1 is cut from the back surface to a thickness of 100 μm.
An approximately n-side electrode is deposited thereon. Thereafter, the p-side electrode and the n-side electrode are alloyed by annealing, and the laser is formed through a cleavage and mounting process.

The semiconductor laser of this embodiment fabricated in this manner is a gain-guided semiconductor laser in which a narrow current path is formed by the current blocking layer 7, and the current blocking layer 7 and the GaAs auxiliary cladding layer. It is also a refractive index guided semiconductor laser utilizing the difference in the refractive index from No. 8.
GaAs auxiliary cladding layer 8 sandwiched between current blocking layers 7
Since the refractive index is high, the light distribution is biased upward. Since the current blocking layer 7 has a lower refractive index than that of the GaAs auxiliary cladding layer 8, the light is confined in the lateral direction. When the thickness of the current blocking layer 7 is increased from 0.5 μm to, for example, 1 μm, and the thickness of the embedded p-type GaAs auxiliary cladding layer 8 is increased from 0.1 μm to 0.5 μm, the light distribution moves further upward. The lateral light confinement can be further enhanced. The light distribution can also be deflected upward by lowering the refractive index of the n-type cladding layer 3 on the substrate side (lower side). In this embodiment, n
The material of the mold cladding layer 3 is AlGaInP;
+ Ga) has a composition ratio of 0.4 to Al
The refractive index can be reduced by increasing the composition ratio.

FIGS. 4 and 5 schematically show a laminated structure of another embodiment of the epitaxial wafer formed from the substrate to the current block layer. The thickness and the like are described on the right side of each layer. I have. The epitaxial wafer of FIG. 4 has a configuration in which the n-side cladding layer is mainly composed of a GaInP layer 53 and a thin AlGaInP layer 54 is added thereon. Therefore, as compared with the first embodiment, the equivalent refractive index of the n-side cladding becomes smaller, and the light distribution approaches the upper and lower portions evenly. As a result, the light confinement effect in the horizontal direction is reduced, but the portion where the light intensity becomes maximum approaches the vicinity of the active layer 55.

In the epitaxial wafer shown in FIG.
The p-side cladding layer is constituted only by the GaInP layer 65. AlGaIn having a lower refractive index compared to the first embodiment
Since there is no P layer, the exudation of light on the p-side increases accordingly. Therefore, the difference in the equivalent refractive index in the horizontal direction increases, and the light confinement in the horizontal direction can be made tight.

In each of the above embodiments, the material of the current blocking layers 7, 58, 66 is AlGaIn.
Although P is used, the composition of Ga may be zero. Further, GaInP is used as the second auxiliary cladding layer 9, but other than AlGaInP, AlInP, AlG
aAs and AlAs can also be used.

In the above embodiment, a groove is formed in the current blocking layer, and the GaAs auxiliary cladding layer is formed in the groove by regrowth. Conversely, the GaAs auxiliary cladding layer is left in a stripe shape, and both sides are formed. The current blocking layer may be formed by regrowth. A specific embodiment will be described below.

An epi as shown in FIG.
7 is covered with a silicon nitride film 80, and FIG.
As shown in FIG. At this time, first, Ga
The GaAs layer 79, the GalnAsP
The layer 78 was selectively etched using phosphoric acid: hydrogen peroxide: water = 5: 1: 40 for 6 minutes. Next, the GaAs auxiliary cladding layer 76 is left, and the Galnp layer 77 is left.
Hydrochloric acid: phosphoric acid: water = 220: 11
Etching was performed for 20 minutes using 0: 165. Further, the GaAs auxiliary cladding layer 76 was etched with the above-mentioned phosphoric acid + hydrogen peroxide-based etchant. Thereafter, using silicon nitride film 80 as a mask, silicon-doped AlGalnP (Al / [Al + Ga] = 0.
2) (n = 2 × 17 cm ⁻³ ) at 1.3 μm and Zn
Doped GaAs (1.5 × 19 cm ⁻³ ) was grown to 0.3 μm. Thereafter, a laser was formed by a normal process. The lateral spread angle of the laser thus obtained was as large as 15 degrees. Although the GaAs auxiliary cladding layer and the etch stopper in this embodiment is 300 °, if the GaAs auxiliary cladding layer and the etching stopper are set to 100 °, the function as the auxiliary cladding layer is not substantially achieved. Actually, when a laser was manufactured in the same manner from this epi having an etch stopper of 100 °, the lateral spread angle was as small as about 10 degrees. This is presumably because the etch stopper did not function sufficiently as an auxiliary cladding layer and a large difference in the refractive index in the lateral direction could not be obtained.

[0019]

As described above, according to the semiconductor laser of the present invention, the AlGaInP current blocking layer is formed on the cladding layer opposite to the substrate so as to sandwich the current path, and is sandwiched between the current blocking layers. Since the auxiliary cladding layer made of GaAs is formed in a portion, the difference in the equivalent refractive index in the lateral direction can be increased, and as a result, the radiation angle in the lateral direction can be increased. Moreover, since the equivalent refractive index difference can be adjusted by changing the composition and thickness of the cladding layer material, the adjustment of the radiation angle in the horizontal direction is easy. As a result, the aspect ratio can be adjusted, and the loss at the time of coupling with the optical fiber can be reduced.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view schematically showing a cross section taken along a plane parallel to a cleavage plane of a semiconductor laser according to an embodiment of the present invention.

FIG. 2 is a table showing a list of materials and the like of each epitaxial layer of the semiconductor laser of FIG. 1;

FIG. 3 is a sectional view showing a state in which a groove is formed in a current block layer in a manufacturing process of the semiconductor laser of FIG. 1;

FIG. 4 is a cross-sectional view schematically showing a laminated structure of an epitaxial wafer when manufacturing a semiconductor laser according to another embodiment of the present invention.

FIG. 5 is a cross-sectional view schematically showing a laminated structure of an epitaxial wafer when manufacturing a semiconductor laser according to still another embodiment of the present invention.

FIG. 6 is a cross-sectional view schematically showing a laminated structure of an epitaxial wafer when manufacturing a semiconductor laser according to still another embodiment of the present invention.

FIG. 7 is a sectional view showing a step in the course of manufacturing a semiconductor laser using the epitaxial wafer of FIG. 6;

[Explanation of symbols]

1, 51, 61, 71: GaAs substrate, 3, 53, 5
4, 63, 73: Lower cladding layer, 4, 55, 64, 7
4 Active layer, 5, 6, 56, 57, 65, 75 Upper cladding layer, 7 Current blocking layer, 8, 76 GaAs auxiliary cladding layer, 9, 77 GaInP second auxiliary cladding layer.

Claims (3)

(57) [Claims] 1. A current block semiconductor laser using GaAs as a substrate and an active layer having a smaller band gap than GaAs. An AlGaInP formed on a main cladding layer opposite to the substrate except for a stripe-shaped current path region. (Including a case where the Ga composition is zero), and a GaAs auxiliary cladding layer formed on the main cladding layer in a stripe-shaped current path region sandwiched between the current blocking layers. Characteristic semiconductor laser. 2. A second auxiliary cladding layer of AlGaInP (including a case where one of Al and Ga is zero) or AlGaAs (including a case where the Ga composition is zero) is further formed on the GaAs auxiliary cladding layer. The semiconductor laser according to claim 1, further comprising: 3. The composition of the main clad layer on the side opposite to the substrate and the composition of the clad layer on the substrate side is adjusted such that the distribution of light in the vertical direction is biased toward the side opposite to the substrate. The semiconductor laser according to claim 1.